Resist compositions are facing new challenges in the field of microelectronic fabrication. The need to mass-produce microscopically dimensioned, etched configurations has resulted in demand for resists with the properties of greater speed, higher contrast and better spectral sensitivity so as to improve image resolution and processing flexibility and reduce the unit cost of the end-product electronic device. ("Speed" as used herein refers to the sensitivity of the composition to activating radiation, and is not to be confused with development rate.)
A useful class of positive-working photoresist compositions comprises a polymer containing recurring groups with pendant quinone diazide groups that are light sensitive, and a dissolution inhibitor monomer that tends to insolubilize the polymer in areas wherein the quinone diazide has not been decomposed by exposure to activating radiation. One of the monomer's functions is to thermally convert to a ketene that causes crosslinking, thereby providing thermal resistance, as is well known. Examples are described in U.S. Pat. No. 4,365,019, wherein the monomer comprises, e.g., 1,3,5-trihydroxybenzene esterified with 1,2-naphthoquinone diazide sulfonic acid (NDS). Examples of particularly useful polymers include the so-called Novolak resins, which are well known. The image/nonimage differential of the diazoketone/Novolak photoresist systems hinges on the principal of dissolution inhibition. Resists based on such diazoketone/Novolak positive-working systems have usually functioned very well, however, they are not completely adequate. The availability of a resist composition having higher speed, higher contrast and better spectral sensitivity would greatly expand the possible chemistries and more closely fit the processing format of some circuit designers.
What then has been needed prior to this invention is a positive-working photoresist composition that is capable of higher speed, higher contrast and better spectral sensitivity than the conventional diazoketone/Novolak systems.